71M6543F Datasheet, PDF (14/157 Pages) Maxim Integrated Products – Selectable Gain of 1 or 8 for One Current Energy Meter ICs Metrology Compensation

71M6543F/H and 71M6543G/GH Data Sheet
Pins IADC0-IADC1 can be programmed individually to be differential or single-ended as determined by
the DIFF0_E (I/O RAM 0x210C[4]) control bit. However, for most applications, IADC0-IADC1 are
configured as a differential input to work with a resistive shunt or CT directly interfaced to the IADC0-
IADC1 differential input with the appropriate external signal conditioning components.
The performance of the IADC0-IADC1 pins can be enhanced by enabling a pre-amplifier with a fixed gain
of 8, using the I/O RAM control bit PRE_E (I/O RAM 0x2704[5]). When PRE_E = 1, IADC0-IADC1 become
the inputs to the 8x pre-amplifier, and the output of this amplifier is supplied to the multiplexer. The 8x
amplification is useful when current sensors with low sensitivity, such as shunt resistors, are used. With
PRE_E set, the IADC0-IADC1 input signal amplitude is restricted to 31.25 mV peak. When PRE_E = 0
(Gain = 1), the IADC0-IADC1 input signal is restricted to 250 mV peak.
For the 71M6543 application utilizing shunt resistor sensors (Figure 2), the IADC0-IADC1 pins are
configured for differential mode to interface to a local shunt by setting the DIFF0_E control bit. Meanwhile,
the IADC2-IADC3 , IADC4-IADC5 and IADC6-IADC7 pins are re-configured as digital remote sensor
interface designed to communicate with a Teridian 71M6xx3 isolated sensor by setting the RMTx_E control
bits (I/O RAM 0x2709[5:3]). The 71M6xx3 communicates with the 71M6543 using a bi-directional digital data
stream through an isolating pulse transformer. The 71M6543 also supplies power to the 71M6xx3 through
the isolating transformer. This type of interface is further described at the end of this chapter. See 2.2.8
71M6xx3 Isolated Sensor Interface.
For use with Current Transformers (CTs), as shown in Figure 3, the RMTx_E control bits are reset, so that
IADC2-IADC3, IADC4-IADC5 and IADC6-IADC7 are configured as local analog inputs. The IADC0-IADC1
pins cannot be configured as a remote sensor interface.
2.2.2 Input Multiplexer
When operating with locally connected sensors, the input multiplexer sequentially applies the input signals
from the analog input pins to the input of the ADC (see Figure 3), according to the sampling sequence
determined by the eleven MUXn_SEL[3:0] control fields. One complete sampling sequence is called a
multiplexer frame. The multiplexer of the 71M6543 can select up to eleven input signals when the current
sensor inputs are configured for single-ended mode. When the current sensor inputs are configured in
differential mode (recommended for best performance), the number of input signals is seven (i.e., IADC0-
IADC1, IADC2-IADC3, IADC4-IADC5, IADC6-IADC7, VADC8, VADC9 and VADC10) per multiplexer frame.
The number of slots in the multiplexer frame is controlled by the I/O RAM control field MUX_DIV[3:0] (I/O
RAM 0x2100[7:4]) (see Figure 4). The multiplexer always starts at state 0 and proceeds until the number
of sensor channels determined by the MUX_DIV[3:0] field setting have been converted.
The 71M6543 requires a unique CE code that is written for the specific meter configuration. Moreover,
each CE code requires specific AFE and MUX settings in order to function properly. Table 1 provides
the CE code and settings corresponding to the 1-Local / 3-Remote sensor configuration shown in
Figure 2. Table 2 provides the CE code and settings corresponding to the CT configuration shown in
Figure 3.
14
© 2008–2011 Teridian Semiconductor Corporation
v1.2